The urine from a non-tobacco user was fortified with analytes to a final concentration of 25 ng/mL and prepared by a liquid-liquid extraction method. A 250 μL urine sample was mixed with 50 μL of 5N NaOH and extracted with 1.5 mL of 50/50 methylene chloride/diethyl ether. A portion of organic phase (1.0 mL) was dried and reconstituted with 200 μL of water for analysis.